330 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. . 
because one adult Calanus is worth many Centropages -or Pseudo- 
calanus in food value, though the latter are an important food for 
fish fry. It is the Calanus swarms which form the chief copepod con- 
stituent of the food of mackerel, pollack, and probably of the shad — 
which summer in the Gulf; and for Calanus as for the volume of plank- 
ton, the richest parts of the Gulf were off Massachusetts Bay and off 
Mt. Desert Rock (Stations 10092, 10100), with a third prolific area 
off Chatham detected by Captain McFarland. 
MICROPLANKTON. 
The microplankton of the cruise will be treated later in special 
reports. But it is worth while to give a brief account of the distribu- 
tion of general plankton types here, because of their bearing on general 
oceanographic problems (Fig. 82). They fall into four general types, 
which may be called “Ceratium,” “diatom,” “mixed” (a mixture of 
the two), and a tropical type characterized by the presence of con- 
siderable amounts of Trichodesmium. Of course these are not 
actually distinct, grading into one another; but they group sufficiently _ 
well to be treated in this way. ‘To take the rarer types first, tropical 
plankton (the “Desmo Plankton” of Cleve) was encountered only 
once, in the inner edge of the Gulf Stream (Station 10071) where 
the rather scanty catch consisted chiefly of Ceratiwm macroceros, and 
of Trichodesmium, with an occasional diatom (Rhizosolenia). Dia- 
tom plankton was encountered in three distinct regions; on George’s 
Bank (Station 10059); off the mouth of Chesapeake Bay (Stations 
10075, 10077, 10078) and in the northern part of the Gulf of Maine 
near Mt. Desert (Stations 10099, 10101). 
The species composing these diatom swarms were quite different 
in these three regions. On George’s Bank the mass, which was rather 
rich, consisted chiefly of a species Guinardia, besides such forms as 
Eucampia zoodiacus, Rhizosolenia stolforthi, and R. styliformis, practi- 
cally a pure diatom haul, except for an occasional Peridinium and 
Ceratium. The diatom swarm off Chesapeake Bay consisted chiefly 
of various species of Chaetoceras (among them C. decipiens and C. 
contortum) with smaller numbers of Rhizosolenia, Leptocylindrus, 
and Thalassiothrix. And at the mouth of the Bay the haul was 
chiefly Rhizosolenia. | 
The diatom plankton found in the Gulf of Maine is difficult to place 
because it was chiefly debris, and evidently moribund. But fragments 
of Rhizosolenia and Chaetoceras decipiens, with other species of Chae- 
